Does the grade of a top affect the sound of the guitar?

[JJDonohue]

One problem is that topwood vendors have non-uniformly dimensioned wood. Getting a reliably quantifiable deflection # is impossible until such time as to get it uniformly and consistently dimensioned. So in the absence of that, we're left with the more subjective tap, scratch and flex method that I've tried to use in at least getting tops into the ballpark.

I also quantify the deflection but only after thicknessing it to .140" and cutting to 8.5" wide. I lay it betweed dowels positioned 18" apart. I then lay a 5lb weight precisely in the center and observe the deflection along the grain using a dial indicator. That stiffness number, along with my subjective method has left me with a pretty good stash of topwood. Having that # helps me to decide on the x-spread as well as the level of brace reinforcement to employ. Granted, it's still a hunch, but it's a more educated hunch with each succeeding guitar when you have a reliable and repeatable method to measure the top's stiffness.

Next question...does anyone bake their tops prior to use?

[tippie53]

I don't bake in the oven but I have a heat blanket that is 18 by 24 and will heat the top and back to 135 degrees for 10 minutes prior to glueing.

[JJDonohue]

I started baking tops about 5 guitars ago and have seen some interesting results. I bake my tops in a homemade oven for 2 hours at 200-225*F. The purpose is to drive off some of the resins and solidify others within the wood. I weigh each .140" thick top before baking and about 1-2 weeks ( after equilibrating to RH conditions) after baking. The surprise is that they lose between 6-10% of their weight prior to baking and actually seem drier, harder and stiffer. The stiffness remains unchanged using my previously stated method but they feel and tap much brighter and with more sustain. Others have reported similar results and I was just wondering if anyone here has any experience.

[Darryl Young]

JJ, that is interesting about baking the tops.....I've wanted to try it. For clarity, are you saying the weight lose is still 6% - 10% 1-2 weeks after baking when the top has had time to reaclimate? If so, that pretty good. I'm wondering if this produces about the same results as kiln drying? That process removes water from within the cell stucture and between the cell walls. My understanding is that air drying only removes moisture from between the cell walls but no moisture from within the cell. Also, as I understand it, once moisture is removed from within the cell, it's gone for good. Maybe this is also what baking in the oven does.

One thing I'll mention about deflection testing that I would like to get your thoughts on. If you are only testing for structural integrity then deflection testing seems to make sense as it tests the stiffness of the wood. If you are seeking consistency in tone, that seems to be a function of stiffness and density so it seems that evaluating stiffness alone doesn't tell the whole story. Chaldni testing of particular vibration modes would reveals a function of both stiffness and density so seems that would be a better fit for judging tone/sound. Thoughts?

Another point. Deflection testing only test the stiffness in one direction. Most tests I've seen are setup to test stiffness along the grain.......which makes sense since that is the stiffness that resists the pull of the strings.....and makes perfect sense for evaluating the structural integrity of the top. As for tone, I would guess that stiffness across the grain is also a factor factor. It would certainly influence the shape/location of the node lines at different vibration modes.

There are particular node patterns where the top vibrates across the grain and another where the top vibrates along the node lines. Maybe the frequency of these vibration modes could be used to calculate the Young's modulus of stiffness along and across the grain. You could probably establish a minimum value for the Young's modulus along the grain so the top would be stiff enough to sustain the pull of the strings. And maybe either the cross grain Young's modulus or the ratio of these two values could be used to select an appropriate top for the size body being built (the assumption being that less cross grain stiffness is needed for a smaller body and more is needed for a larger body). I'm guessing that finding the right ratio of cross grain stiffness to stiffness along the grain helps dictate the shape and location of the main frequency of the top (also influenced by the bracing pattern). Maybe you could use this to maximize the area of top movement (and thus power) of the monopole mode which is a large influence on the sound across a broad frequency range of the guitar.

[kencierp]

At one time, maybe still Taylor baked or at least heated their sound-boards --- not sure if they still do?

[Tony_in_NYC]

Roger Siminof developed a method for "tap tuning" his tops by using deflection testing instead of tapping. His theory was that once a top was tuned properly, you could measure the deflection of the top and repeat the tuning on another top by measuring only the deflection. He did this because in one environment he worked in there was a machine that caused the tuner he was using to get false readings. By using only the deflection, he could get repeatable results time after time no matter what noises were present.
The caveat to this it that he tested the deflection of a fully braced top and shaved the braces to achieve the deflection he was looking for. It was not just a plate without braces.

[Tom West]

Guitar Hack: A lot of grading is based on visual appeal.While most of the higher grades will make excellant tops there are lots of lesser grades not as nice looking wood that will make excellant tops. Stiffness and light weight with little or no runout and a good musical tap tone with sustain are general qualities I look for in top wood. Some folks have been know to select thier top wood blindfolded to not be influenced by the look of the wood. Someone mentioned John at Old World Tonewoods and I must say he has good wood at a resonable price. John Hall is right in saying trust one of the well known dealers to get your wood. Touch,examine,feel and tap as many tops as you can get your hands on and you will gradually develop a better ability to select the best wood. All part of the skill set you should develop if you plan to continue to build more guitars. Good luck.
Tom